Uranium activated fluorescent materials



United States Patent 3,457,179 URANIUM ACTIVATED FLUORESCENT MATERIALS Samuel Natansohn, Massapequa Park, N.Y., assignor to General Telephone & Electronics Laboratories Incorporated, a corporation of Delaware No Drawing. Filed Dec. 6, 1967, Ser. No. 688,312 Int. Cl. C09k 1/62, 1/04 US. Cl. 252301.1 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to fluorescent materials which emit a green luminescence when exposed to ultraviolet, cathode ray or X-ray radiation and, in particunlar, to uranium activated phosphors wherein the host component comprises lithium and magnesium oxide compounds combined with tetravalent, pentavalent and/or hexavalent metal oxide compounds.

US. Patent 2,785,137 discloses luminescent materials comprising a matrix of the elements magnesium, lithium, antimony and oxygen, the matrix being activated by manganese or uranium or both. These materials are prepared by mixing oxide compounds of magnesium, lithium and antimony with compounds of manganese and/ or uranium, and then firing the mixture at a temperature in the range 700 C. to 1250 C. When activated with managnese the material emits a deep red luminescence under excitation by ultraviolet light. When activated with uranium and excited under the same conditions, the phosphor emits a green luminescence.

SUMMARY OF THE INVENTION The present invention comprises a phosphor consisting essentially of compositions defined by the formula 2 )X( g (A Z)Z( 3)Z( 2 5)1 z= WU Where A is a tetravalent metal ion selected from the group consisting of Ti, Zr, Hf, Ge, Sn and Pb; B is a hexavalent metal ion selected from the group consisting of Mo, Te and W; C is a pentavalent metal ion selected from the group consisting of Nb, Sb and Ta; x is between 2 and 6; x+y=8; z is greater than zero and does not exceed 1; and w has a value selected to produce fluorescence when the composition is excited by ultraviolet, cathoderay or X-ray radiation. More specifically, w has a value in the range 0.005 to 0.10 gram-atom per gram-atom of the host (Li O) (MgO) (AO (BO (C O with maximum luminescence being obtained for a value of w of about 0.02.

The invention also includes phosphor compositions in which z=0 and C is selected from the group consisting of Nb and Ta It is believed that the actual luminescence centers in the described compositions consist of uranium ions coordinated by several oxygen ions in the host matrix. The luminescence from these uranium-oxygen centers is similar to that attributed to electronic transitions within the molecular uranyl ion, UO Thus, while the subject phosphors are believed best defined as uranium activated, they may also be considered as uranyl activated.

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The subject phosphor compounds are preferably prepared by mixing the appropriate amounts of lithium carbonate and the appropriate oxides of the aforementioned metals of Groups IV, V, and/or VI of the Periodic Table. Alternately, compounds which yield the desired oxides upon thermal decomposition may be substituted for the lithium and magnesium carbonates and the oxides of the Groups IV, V and VI elements. The uranium activator is added in the form of a uranyl salt such as a nitrate or acetate.

In the synthesis of compounds containing antimony, the trioxide of antimony Sb O in which the antimony is in the 3+ is used and during the fixing process the anti mony is oxidized to the 5+ state. In the preparation of compounds containing niobium or tantalum the pentoxides Nb O and Ta O respectively are used.

The mixture of the component materials is heated in air in a series of steps at elevated temperatures, the sample being ground in a mortar between the firing steps. The optimum firing temperature depends on the thermal stability of the compound and, for most of the disclosed compounds, is in the range l200 to 1400 C.

All of the subject compounds emit green light having an emission peak between 520 and 525 nanometers with a half-line width of 35 to 40 nanometers when excited by ultraviolet or cathode ray radiation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I 6.65 grams of liihium carbonate Li CO 13.95 grams of basic magnesium carbonate, 7.97 grams of niobium pentoxide Nb O and 0.1273 gram of uranyl acetate UO (C H O -2H O were mixed thoroughly and fired sequentially in alumina crucibles at 800 C., 1100 C., 1200 C. and 1300" C. Each firing was carried out for a period of about 4 hours, the sample being cooled and ground between firing steps. The resulting phosphor Li Mg Nb O 0.01 U emits green light when excited by ultraviolet or cathode-ray radiation, the emission peak being at 525 nanometers with a half width of 35 nanometers.

Example II 8.87 grams of lithium carbonate, 11.01 grams of basic magnesium carbonate, 13.25 grams of tantalum pentoxide Ta O and 0.1273 gram of uranyl acetate were mixed thoroughly and fired in alumina crucibles at 800 C., 1100 C. and 1300 C. Each firing was carried out for a period of about 4 hours, the samples being cooled and ground between firing steps. The resulting phosphor Li Mg Ta O 0.01U emits green light with an emission peak at 5 20 nanometers and a half width of 40 nanometers when excited by ultraviolet or cathode-ray radiation.

Example III 6.65 grams of lithium carbonate, 13.77 grams of basic magnesium carbonate, 4.38 grams of antimony trioxide Sb O 1.57 grams of germanium dioxide GeO 3.48 grams of tungsten trioxide W0 and 0.2545 gram of uranyl acetate were mixed thoroughly and then fired in alumina crucibles at 800 C., 1000 C., 1100 C., 1200 C. and 1300" C. The firing times were approximately the same as in Examples I and II, and the material was ground between firings. The resulting phosphor 0.02UO emits green light with an emission peak at 520 nanometers and a half-line width of 35 nanometers when excited by ultraviolet and cathode-ray radiation.

3 Example IV 6.65 grams of lithium carbonate, 13.77 grams of basic magnesium carbonate, 4.38 grams of antimony trioxide,

emission peak in the 520525 nanometer range and half line widths of 35-40 nanometers. The mixtures-used to produce these phosphors and the optimum maximum firing temperature are given in Tables I and II.

TABLE I h Basie Lithium magnesium Uranyl Optimum Composition carbonate carbonate acetate Oxide of A Oxide of B Oxide of O firing temp. Li h Ig AzB=C2(tz WU (grams) (grams) 1 (gram) (grams) (grams) (grams) C.)

LioMgrHimTeo sbo g: 0.02U 6. 65 13. 77 0. 2545 HfOz'. 3.15 TG(OH)5Z 3.44 Sbz 4.38 1,400 LieMgG00.5TGo.5SbO 3. 0.02U 6. 65 13. 77 0. 2545 GeOz: 1.57 Te(OI-I)e: 3.44 Sbz0 4.38 1, 300 Li6Mg Tio.rTeo.5SbO13Z 0.02U 6. 65 13. 77 0. 2545 T1022 1.20 Te(OH)eI 3.44 813203: 4.38 1, 300 Li6Mg5Pbo.5Teo.5SbO 3t 0.02U 6. 65 13. 77 0. 2545 PbOzZ 3.59 Te(OH)a: 3.44 SbzO 4.38 1, 100 LiuMg Zr Teo.5SbO 3: 0.02U. 6. 65 14. 17 0. 2545 ZrOz: 1.85 Te(OH)a: 3.44 SbzOaI 4.38 1, 300 LiuMg S11u.5Wu5SbO13: 0.02U 6. 65 13. 77 0. 2545 SnOz: 2.26 W03: 3.48 Sbz0 4.38 1,400 Li6lvlg Hfu.5\V0.5SbO 0.02U 6. 65 13. 77 0. 2545 H102: 3.15 W03: 348 SbzOa: 4.38 1,400 LiaMg5Ti0.5W SbO 0.02U 6. 65 13. 77 0. 2545 'IiOz: 1.20 W03: 3 48 513203: 4.38 1, 300 Lia1VIg5Pbc.5Wo.5SbO a: 0.02U 6. 65 13. 77 0. 2545 PbOz: 3.59 W03: 3.48 313203: 4.38 1,100 LiaMg5Z1'0.5W0.5SbO1a: 0.02U 6. 65 14.17 0. 2545 ZrOz: 1.85 W0 3.48 SbzOg: 4.38 1,400

1 The variations in the amounts of basic magnesium carbonate used reflect changes in the magnesium content in different lots of this nonstoichio metric material.

TABLE II Basic Lithium magnesium Uranyl Optimum Composition carbonate carbonate acetate Oxide of A Oxide of B Oxide of O firing temp. L12 hIgy-AzBzCR(1z): WU (grams) (grams) 1 (gram) (grams) (grams) (grams) C.)

LiuMg SnTeO a: 0.02U 6. 65 13. 77 0. 2545 EH02: 4.52 T(OH)0Z 6 1, 200 LirMg5HtTe0g: 0.02U 6. 65 13. 77 0. 2545 HiOz: 6.30 Te(OH)u: 6 1, 300 LiaMgaGcTeoia: 0.02U... 6. 65 13. 77 0. 2545 GeOi: 3.14 'Ie(OH)6: 6 1, 300 LieMgsTiTeoiai 0.02U 6.05 13. 77 0. 2545 T1022 2.40 Tc(OH) 6 1, 300 LiqMg5PbTeO 3: 0.02U. 6. 65 13. 77 0.2545 PbOz: 7.18 TO(OH)a. 6 1,000 LiqMg5SnWOn: 0.02U 6. 65 13. 77 0. 2545 S1102! 4.52 W03: 6.06 1,200 LiuMgsGewO z: 0.02U 6. 65 13. 77 0. 2545 GeOz: 3.14 W03: 6.96 1,200 LiaMg5TiWO13: 0.02U 6. 65 13. 77 0. 2545 T101: 2.40 W03 6.96 1,300 LinMg5PbWO 3: 0.02U. 6. 65 13. 77 0. 2545 PbOn: 7.18 W03 6.96 1,100 LiEMg5ZrWO 3: 0.02U 6. 65 14.17 0. 2545 ZrOz: 3.70 W03 6.96 1, 200 LisMg4Nb2O 32 0.01U 8.87 11. 01 0.1273 1, 300 LieMg Zr Mo Nb0 0 01U 6. 65 13. 77 0.1273 ZrOz: 1.85 M003: 2.16 1, 300 LiuMgsTazOiaz 0.01U 6. 65 13.95 0.1273 TazO5: 13.25 1,200 LiuMg5Hf0.5Wo.5TaO1a: 0.01U 6. 65 13. 77 0.1273 HiOz: 3.15 W03: 3.48 T21120 13.25 1, 300

1 See note to Table I.

2.26 grams of tin dioxide, SnO 3.44 grams of orthotelluric acid Te(OH) and 0.2545 gram of uranyl acetate were mixed thoroughly and fired in alumina crucibles at 800 C., 1000 C. and 1200 C. for a period of 4 hours each and at 1300 C. and 1400 C. for a period of approximately 1 hour each. The resulting phosphor 0.02U emits green light with an emission peak at 520 nanometers and a half-line of 40 nanometers upon excitation by ultraviolet or cathode-ray radiation.

Example V 6.65 grams of lithium carbonate, 13.77 grams of basic magnesium carbonate, 6.30 grams of hafnium dioxide, HfO 6.96 grams of tungsten trioxide, and 0.2545 gram of uranyl acetate were mixed and fired in alumina crucibles at 800 C., 1000 C., 1100 C. and 1200 C. As in the previous examples the phosphors were ground between firings and were fired for periods of approximately 4 hours. The resulting phosphor Li Mg HfWO 0.02U emits green light peaking at 520 nanometers with a half-line width at 40 nanometers under ultraviolet or cathode-ray radiation.

Example VI A number of other compositions were prepared by the same general method as described for Examples I to V1. All of these phosphors emitted green light with the same approximate spectral characteristics. When excited by ultraviolet or cathode-ray radiation they exhibited an Summarizing, uranium activated phosphor compounds have been disclosed wherein the host components consist of lithium and magnesium oxides combined with oxides of selected tetravalent, hexavalent and pentavalent metal 40 ions. These phosphors may be used for color correction in high pressure mercury lamps and other fluorescent discharge devices and as the green-emitting phosphor in color cathode ray tube screens.

As many changes could be made in the above described compositions and many different embodiments could be made without departing from the scope thereof, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A phosphor consisting essentially of compositions defined by the formular 2 )X( )y( 2)z( 3)z( z 5)1 Z where A is a tetravalent metal ion selected from the group consisting of Ti, Zr, 'Hf, Ge, Sn and Pb, B is a hexavalent metal ion selected from the group consisting of M0, Te, and W, C is a pentavalenet metal ion selected from the group consisting of Nb, Sb, and Ta, x is between 2 and 6 and x+y=8, z is greater than zero and does not exceed 1, and w has a value selected to produce fluorescence when the composition is excited by ultraviolet, cathode-ray or X-ray radiation.

2. The phosphor defined by claim 1 wherein w has a value between 0.005 and 0.10 gram-atom per gram-atom of the host.

3. The phosphor defined by claim 1 wherein A is Ge, B is W, C is Sb, x=3, y=5, z=0.5 and w=0.02.

4. The phosphor defined by claim 1 wherein A is Sn, B is Te, C is Sb, x=3, y=5, 2:0.5 and w=0.02.

5. The phosphor defined by claim 1 wherein A is Hf,

B is W, x=3, y=5, z=1, and w=0.02.

6. The phosphor defined by claim 1 wherein A is Zr, B is Te, x=3, y=5, 2:1 and w=0.02.

7. A phosphor consisting essentially of compositions defined by the formula (Li O) (MgO) (C 0 ):wU

5 6 where C is a pentavalent metal ion selected from the 2,225,704 12/ 1940 McKeag 252301.5 group consisting of Nb and Ta, x is between 2 and 6 and 2,558,913 7/1951 Rice 25230l.5 x+y =8 ,and w has a value between 0.005 and 0.10 gram- 2,785,137 3/ 1957 Ranby 252301.4 atom per gram-atom of the host 2,865,862 12/ 1958 Mooney 252301.5 (Li2O)x(MgO)y(C2O5) :WU 5 3,218,262 11/1965 La arte 252301.1

8. The phosphor defined by claim 7 wherein C is Nb, BENJAMIN R PADGETT Primary Examiner x=3, y=5, and w=0.01.

9. The phosphor defined by claim 7 wherein C is Ta, L SCOLNICK, Assistant Examiner x=4, y=4, and w=0.01. 10

References Cited UNITED STATES PATENTS 252--301.4, 301.5

2,182,087 12/ 1939 Leverenz 25230l.1 

